Merely mentioning a term doesn't mean you have to put the trademark symbol on it, you know that. There's zero legal requirement for any company (even the holder) to display the symbol. It is considered good legal practice for a holder to display it at least once per document/page, but legally not actually required to display it in every instance.
But you're confusing what Strava does with what Shimano is doing. Strava is displaying a metric and calling it X (as opposed to a TrainingPeaks branded metric). I agree that if those metrics exactly match, then that's shades of grey.
But Shimano isn't displaying anything. They don't have any software that displays anything, nor even any hardware that displays anything. They're merely mentioning that you could use such metrics, but you'd still need to go out and buy some device/platform/whatever that displays those. Of which they make none (you do however).
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My tiny little slice of the internets:
dcrainmaker.com